The substantia nigra, pars compacta (SNc) is a structure that modulates voluntary motor control, and the death of the dopaminergic neurons in the SNc leads to many of the classic motor deficits associated with the Parkinson's disease (PD). Most conventional treatments alleviate symptoms but do not prevent the eventual death of neurons in the SNc. While fetal tissue transplant and stem cell therapy serve to replace lost cells, incomplete knowledge on dopamine neuron development within the SNc has limited the effectiveness of these treatments as most cells in the transplant fail to survive. Elucidating the factors that modulate dopamine neural development could lead to novel treatment approaches or increase the effectiveness of these replacement therapies in PD. In the rat brain, progesterone receptors (PRs) are expressed transiently in the perinatal SNc, suggesting a role for this hormone in the development of this region. Dr. Mennella proposes to characterize the temporal expression pattern of progesterone receptors in the mouse substantia nigra and determine their roles in the morphological and phenotypic development of that region. She also proposes to use PR knock-out (PRKO) mice to determine if absence of PRs during development leads to greater dopaminergic cell loss in the adult SNc, and more immature projections into the straitum, the primary recipient of SNc dopamine projections and greater motor deficits in adulthood.